Silicon structure, method for manufacturing the same, and sensor chip

ABSTRACT

A silicon structure of the present invention is provided with a silicon substrate ( 1 ) to become a base, and a plurality of fibrous projections ( 2 ) made of silicon dioxide and directly joined to a silicon-made surface ( 1   a ) of the silicon substrate ( 1 ). By arbitrarily constructing an area where these fibrous projections ( 2 ) are formed in a predetermined area, it is possible to render the area to have at least either hydrophilicity or water retentivity, so as to provide a silicon structure useful for a variety of devices.

TECHNICAL FIELD

The present invention relates to a silicon structure required to have atleast either hydrophilicity or water retentivity, a method formanufacturing the same, and a sensor chip, having a silicon structureand being used for a cellular electrophysiological sensor, of a varietyof sensors, actuators, electronic devices and the like, which usesilicon.

BACKGROUND ART

Recently, an MEMS (Micro Electro Mechanical Systems) device using asilicon material for measuring a biochemical reaction has become a focusof attention.

For example disclosed has been a technique of providing plural throughholes in a cell holding substrate, making a sample cell closely adhereto an opening of the through hole, and measuring a potential-dependention-channel activity of the sample cell with a measurement electrodearranged below the through hole.

Further disclosed has been a technique of forming a 2.5-μm through hole(hole) inside a cell holding substrate (membrane) made of silicon oxide,and making this through hole hold HEK293 cell as a kind of humancultured cell lines, to ensure high adhesiveness and measure anextracellular potential with high accuracy (e.g., refer to Non-PatentDocument 1).

For such a structure used for such a cell holding substrate, a siliconmaterial broadly in use in the field of the semiconductor technology ispreferably used from the viewpoints of processability and productivity.

The surface of the silicon material used for a device made up of such astructure preferably has hydrophilicity or water retentivity, and insome cases, it is required to have both the hydrophilicity and the waterretentivity. For the purpose of making the surface of the siliconmaterial hydrophilic, a technique of forming a thin film of an inorganicoxide on the surface of the silicon material by sputtering has beendisclosed (e.g., refer to Patent Document 1).

However, with the conventional configuration, imparting thehydrophilicity has been possible, but imparting the water retentivityhas not been possible. Further, although it is required to form an areahaving the hydrophilicity or the water retentivity in a restrictedspecific area, it has been particularly difficult to form the areahaving the water retentivity in a restricted area.

Incidentally, living matters including humans organize a variety ofcells to conduct activities. As a mechanism for transmitting stimulusinformation, received by a cell (e.g. visual cell) in some tissue fromthe outside, to another tissue cell (e.g. nerve), ion channels arepresent as a kind of functional proteins. These ion channels reside incell membranes of every kind, and undertake an important role ofallowing passage of ions (e.g. Na⁺, K⁺, Ca²⁺, etc.) between the insideand outside of the cell, to generate a current to be transmitted betweencells or a potential difference.

In recent years, it has become possible, by finding out details ofactions of these ion channels, to measure an effect of a new medicine ata cellular level or to measure the presence or absence of a side effect.While a variety of methods for measuring ion channels are present, apatch clamp technique has been the most used method since being capableof accurately measuring actions of ion channels in a single cell. Amongthe back clamp techniques, a planar patch technique capable of holdingcells on a plane substrate has been a great focus of attention as beingeffective in increasing a throughput of measurement.

In this planer patch technique, a cellular electrophysiological sensoris used as a sensor portion for holding and electrically measuring acell. As a sensor chip for this cellular electrophysiological sensor,the foregoing structure using the silicon material (hereinafter referredto as a “silicon structure”) can be employed.

An example of conventional cellular electrophysiological sensors isdescribed in further details. FIG. 37 shows a sectional view of aconventional cellular electrophysiological sensor. As shown in FIG. 37,sensor chip 201 for the cellular electrophysiological sensor is providedwith thin plate 203 having conduction hole 202, and frame body 204arranged on this thin plate 203, and has cavity 205 inside frame body204. Further, these thin plate 203 and frame body 204 have beenprocessed using silicon material with high accuracy.

The cellular electrophysiological sensor using this sensor chip 201 isprovided with: chip holding plate 206 with sensor chip 201 insertedtherein; electrolytic baths 207, 208 arranged above and below sensorchip 201; and electrodes 209, 210 respectively arranged inside theseelectrolytic baths 207, 208.

In this cellular electrophysiological sensor, each of electrolytic baths207, 208 is filled with an electrolyte, and cells 211 are then injectedinto upper electrolytic bath 207. Subsequently, by absorbing theelectrolyte or the like downward from lower electrolytic bath 208 orperforming some other operation, cell 211 can be captured at an openingof conduction hole 202. A potential difference between electrolyticbaths 207, 208, a current, a resistance or the like can then bemeasured, so as to measure physicochemical changes during activities ofcells 211, namely actions of ion-channels.

Here, it is required in the measurement that each of top and undersurfaces of sensor chip 201 be filled with the electrolyte. However,since the surface is made of a hydrophobic silicon base, it is difficultto fill the inside of cavity 205 with the electrolyte. Therefore, as amethod for rendering sensor chip 201 hydrophilic, there exists a methodof thermally treating sensor chip 201 to form hydrophilic thermallyoxidized film 212 on the surface of the silicon base.

It is to be noted that a similar example to above sensor chip 201 isdisclosed in Patent Document 2 mentioned below.

However, there has been a problem with conventional sensor chip 201 inthat measurement accuracy of the cellular electrophysiological sensormay decrease.

The reason for this is that bubble 213 may be generated inside cavity205 of frame body 204 depending upon a difference in environment wheremeasurement is performed.

Specifically, even when thermally oxidized film 212 is formed on aninner wall of frame body 204, an organic matter or the like adheres tothe surface of the film with time, to lower the hydrophilicity. Thismakes bubble 213 apt to be generated inside cavity 205, and due to thepresence of bubble 213, electrical conduction between the above andbelow conduction hole 202 is inhibited, or infiltration of a medicine isinhibited. As a consequence, there has been a problem in that themeasurement accuracy of the cellular electrophysiological sensordecreases.

Moreover, another example of the conventional cellularelectrophysiological sensors is described in further details. FIG. 38shows a sectional view of a conventional cellular electrophysiologicalsensor. As shown in FIG. 38, sensor chip 301 for the conventionalcellular electrophysiological sensor is provided with thin plate 303having conduction hole 302, and frame body 304 arranged on this thinplate 303, and these thin plate 303 and frame body 304 have beenprocessed using the silicon material with high accuracy.

Cellular electrophysiological sensor 305 using this sensor chip 301 isprovided with: chip holding plate 306 with sensor chip 301 insertedtherein; electrolytic baths 307 a, 307 b arranged above and below sensorchip 301; and electrodes 308 a, 308 b respectively arranged inside theseelectrolytic baths 307 a, 307 b.

In this cellular electrophysiological sensor 305, each of electrolyticbaths 307 a, 307 b is filled with an electrolyte, and cells 309 are theninjected into upper electrolytic bath 307 a. Subsequently, by absorbingthe electrolyte or the like downward from lower electrolytic bath 307 bor performing some other operation, cell 309 can be captured at anopening of conduction hole 302. A potential difference betweenelectrolytic baths 307 a, 307 b, a current, a resistance or the like canthen be measured, so as to measure physicochemical changes of cells 309during activities of cells 309, namely actions of ion-channels.

Here, it is required that each of top and under surfaces of sensor chip301 be filled with the electrolyte. However, since the surface is madeof a silicon base that is apt to be hydrophobic, a bubble may begenerated on the under surface of sensor chip 301. As a method forrendering the surface of sensor chip 301 hydrophilic to preventgeneration of this bubble, there exists a method of thermally treatingsensor chip 301 to form hydrophilic thermally oxidized film 310 on itssurface.

It is to be noted that a similar example to above sensor chip 301 isdisclosed in Patent Document 1 mentioned below.

However, there has been a problem with conventional sensor chip 301 inthat measurement accuracy of cellular electrophysiological sensor 305may decrease.

The reason for this is that a bubble may be generated on under surface303 a of thin plate 303 depending upon a difference in environment wheremeasurement is performed.

Specifically, even when thermally oxidized film 310 is formed on undersurface 303 a of thin plate 303, an organic matter or the like adheresto the surface of the film with time, whereby the hydrophilicitydecreases and bubble 312 is then generated. When, as a consequence, thisbubble 312 adheres to the vicinity of lead-out port 311 of conductionhole 302, electrical conduction between above and below conduction hole302 is inhibited.

Consequently, there has been a problem in that the measurement accuracyof cellular electrophysiological sensor 305 decreases.

-   [Non-Patent Document 1] “Micro Total Analysis Systems 2004”, T.    Sordel et al., pp-521-522 (2004)-   [Patent Document 1] Unexamined Japanese Patent Publication No.    2000-243700-   [Patent Document 2] Unexamined Japanese Patent Publication No.    2004-69309

DISCLOSURE OF THE INVENTION

The present invention provides a silicon structure, which is providedwith fibrous projections made of silicon dioxide on its surface made ofsilicon, to selectively form an area having at least eitherhydrophilicity or water retentivity, and a method for manufacturing thesame.

Further, the present invention provides a sensor chip, including asilicon structure and capable of improving measurement accuracy of acellular electrophysiological sensor.

Specifically, a silicon structure of the present invention includes abase, and plural fibrous projections made of silicon dioxide on asilicon-made surface of this base, and these plural fibrous projectionsare configured to be directly joined to the surface.

In this manner, one ends of the fibrous projections made of silicondioxide are formed by direct joining on the surface of the siliconstructure, whereby an area where these fibrous projections are formed isconfigured to selectively have at least either hydrophilicity or waterretentivity.

Further, a method for manufacturing a silicon structure according to thepresent invention includes: a first step of forming a seed layer made ofan organic polymer in an arbitrary area on a silicon-made surface of abase; and a second step of heating the base in an oxygen atmosphere, toform plural fibrous projections made of silicon dioxide in the areawhere the seed layer is formed.

With such a method performed, the plural fibrous projections can beformed by direct joining in a predetermined area on the surface of thebase, so that silicon dioxide that forms the plural fibrous projectionshas a large surface area. It is thereby possible to manufacture asilicon structure capable of exerting at least either hydrophilicity orwater retentivity which is high as a whole.

Further, a sensor chip in the present invention is provided with: a thinplate having a conduction hole; and a frame body arranged on this thinplate, a cell capturing face of the thin plate is formed of a silicondioxide layer, while an inner wall of the frame body is formed of asilicon layer, and plural fibrous projections made of silicon dioxideare directly joined to the inner wall of the frame body.

With such a configuration formed, the fibrous projections having thehydrophilicity and a very large surface area are provided on the innerwall of the frame body so that bubbles which are generated inside acavity of the frame body can be reduced. Therefore, using the sensorchip of the present invention for a cellular electrophysiological sensoror the like can significantly improve the measurement accuracy.

Further, a sensor chip of the present invention is provided with: a thinplate having a conduction hole; and a frame body arranged on this thinplate, the thin plate is made up of a laminated body of a silicon layerand a silicon dioxide layer formed on this silicon layer, and pluralfibrous projections made of silicon dioxide are directly joined to theunder surface of the silicon layer.

With such a configuration formed, fibrous projections having thehydrophilicity and a very large surface area are provided on the undersurface of a thin plate so that bubbles which are generated on the undersurface can be reduced. Therefore, using the sensor chip of the presentinvention for a cellular electrophysiological sensor or the like cansignificantly improve the measurement accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a silicon structure in a first embodimentof the present invention.

FIG. 2 shows an SEM (Scanning Electron Microscope) photograph of asurface of the silicon structure in the first embodiment of the presentinvention.

FIG. 3 is a diagram showing a result of an X-ray analysis on fibrousprojections of the silicon structure in the first embodiment of thepresent invention.

FIG. 4 is a sectional view for explaining a method for manufacturing thesilicon structure in the first embodiment of the present invention.

FIG. 5 is a sectional view for explaining the method for manufacturingthe silicon structure in the first embodiment of the present invention.

FIG. 6 is a sectional view for explaining the method for manufacturingthe silicon structure in the first embodiment of the present invention.

FIG. 7 is a sectional view for explaining the method for manufacturingthe silicon structure in the first embodiment of the present invention.

FIG. 8 is a sectional view for explaining the method for manufacturingthe silicon structure in the first embodiment of the present invention.

FIG. 9 is a sectional view for explaining another method formanufacturing the silicon structure in the first embodiment of thepresent invention.

FIG. 10 is a sectional view for explaining another method formanufacturing the silicon structure in the first embodiment of thepresent invention.

FIG. 11 is a sectional view for explaining another method formanufacturing the silicon structure in the first embodiment of thepresent invention.

FIG. 12 is a sectional view for explaining another method formanufacturing the silicon structure in the first embodiment of thepresent invention.

FIG. 13 is a sectional view of a cellular electrophysiological sensor ina second embodiment of the present invention.

FIG. 14 is a sectional view of a sensor chip in the second embodiment ofthe present invention.

FIG. 15 is a sectional view showing a manufacturing step for the sensorchip in the second embodiment of the present invention.

FIG. 16 is an enlarged sectional view of a main part, showing amanufacturing step for the sensor chip in the second embodiment of thepresent invention.

FIG. 17 is a sectional view of the sensor chip in the second embodimentof the present invention.

FIG. 18 is an enlarged sectional view of the main part, showing amanufacturing step for the sensor chip in the second embodiment of thepresent invention.

FIG. 19 is an enlarged sectional view of the main part, showing amanufacturing step for the sensor chip in the second embodiment of thepresent invention.

FIG. 20 is an enlarged sectional view of the main part, showing amanufacturing step for the sensor chip in the second embodiment of thepresent invention.

FIG. 21 is an enlarged sectional view of the main part, showing amanufacturing step for the sensor chip in the second embodiment of thepresent invention.

FIG. 22 is an enlarged sectional view of the main part, showing amanufacturing step for the sensor chip in the second embodiment of thepresent invention.

FIG. 23 is an enlarged sectional view of the main part, showing amanufacturing step for the sensor chip in the second embodiment of thepresent invention.

FIG. 24 is an enlarged sectional view of the main part, showing amanufacturing step for the sensor chip in the second embodiment of thepresent invention.

FIG. 25 is an enlarged sectional view of the main part, showing amanufacturing step for the sensor chip in the second embodiment of thepresent invention.

FIG. 26 is a sectional view of a sensor chip in a third embodiment ofthe present invention.

FIG. 27 is a sectional view of a cellular electrophysiological sensor ina fourth embodiment of the present invention.

FIG. 28 is a sectional view of a sensor chip in the fourth embodiment ofthe present invention.

FIG. 29 is a sectional view showing a manufacturing step for the sensorchip in the fourth embodiment of the present invention.

FIG. 30 is a sectional view showing a manufacturing step for the sensorchip in the fourth embodiment of the present invention.

FIG. 31 is a sectional view showing a manufacturing step for the sensorchip in the fourth embodiment of the present invention.

FIG. 32 is a sectional view showing a manufacturing step for the sensorchip in the fourth embodiment of the present invention.

FIG. 33 is a sectional view showing a manufacturing step for the sensorchip in the fourth embodiment of the present invention.

FIG. 34 is a sectional view showing a manufacturing step for the sensorchip in the fourth embodiment of the present invention.

FIG. 35 is a sectional view of a sensor chip in a fifth embodiment ofthe present invention.

FIG. 36 is a sectional view showing a manufacturing step for the sensorchip in the fifth embodiment of the present invention.

FIG. 37 is a sectional view of a conventional cellularelectrophysiological sensor.

FIG. 38 is a sectional view of another conventional cellularelectrophysiological sensor.

REFERENCE MARKS IN THE DRAWINGS

1, 6 Silicon substrate (Base)

1 a, 6 a Surface

1 b, 6 b Predetermined area

2, 7, 22, 121 Fibrous projections

3, 8 Resist film

4, 28, 128 Seed layer

5 Silicon dioxide thin film

14, 113 Sensor chip

15, 114 Thin plate

16, 115 Frame body

16 a Inner wall

17, 116 Cavity

18 Second Silicon layer (Silicon layer)

19, 113 a Cell capturing face

20, 118 Silicon dioxide layer

21, 120 Conduction hole

23, 122 Chip holding plate (Holding plate)

24 a, 24 b, 123 a, 123 b Electrolytic bath

25 a, 25 b, 124 a, 124 b Electrode

26, 125 Cell

27 First silicon layer (Silicon layer)

29, 31, 130, 133 Protective layer

30 Thermally oxidized film

117, 126 Silicon layer

117 a Under surface

119 Concave section

120 a Opening

120 b Lead-out port

127 Mask

129 Area where fibrous projections are desired to be left

131 Area where fibrous projections are desired to be removed

132 Area where fibrous projections are not to be formed

PREFERRED EMBODIMENTS FOR CARRYING OUT OF THE INVENTION

An embodiment of the present invention is described below with referenceto the drawings. It is to be noted that, since like elements are denotedby like reference numerals, there are cases where their description isomitted.

First Embodiment

Hereinafter, a silicon structure and a method for manufacturing the sameaccording to a first embodiment of the present invention are describedwith reference to the drawings.

FIG. 1 is a sectional view of a silicon structure in the firstembodiment of the present invention, and FIG. 2 is an SEM photographshowing the surface state of the silicon structure of FIG. 1. Those thatare white and densely formed as entwined with one another are fibrousprojections 2.

As shown in FIGS. 1 and 2, the silicon structure of the presentinvention is provided with: base 1; and plural fibrous projections 2which are made of silicon dioxide and directly joined to silicon-madesurface 1 a of this base 1. Here, base 1 may be a substrate containingsilicon, and in the present embodiment, for example, silicon substrate 1is used. It is to be noted that one ends of fibrous projections 2 aredirectly joined to surface 1 a of silicon substrate 1. In this manner,fibrous projections 2 made of silicon dioxide are formed in moquetteform or mesh form as plural fibrous projections 2. Therefore, in thisarea, a surface area of silicon dioxide is extremely large. In such anarea having a large surface area, a liquid material to which largesurface tension of silicon dioxide is applied, such as water, isstrongly pulled to the surface of silicon dioxide, and the water is thenheld on a periphery of fibrous projections 2.

Next described is a reason for fibrous projections 2 in the firstembodiment of the present invention having large hydrophilicity andwater retentivity. Silicon dioxide is essentially a highly hydrophilicmaterial. However, when silicon dioxide is formed into a thin film andcontamination from the outside such as air adheres to its surface,surface tension of the thin film made of silicon dioxide, which pullswater, decreases. Therefore, when the thin film has a small surfacearea, this results in relatively a considerable loss of thehydrophilicity.

As opposed to this, fibrous projections 2 in the silicon structure shownin FIGS. 1 and 2 of the first embodiment of the present invention havean extremely large surface area. For this reason, even when the surfacetension per predetermined area decreases due to adhesion ofcontamination, the tension that pulls water is hardly lost since thewhole surface area is large. Consequently, it is possible to realize asilicon structure capable of holding the hydrophilicity and the waterretentivity for a long period of time.

Further, fibrous projections 2 are formed by direct joining on thesurface of silicon substrate 1, whereby it is possible to simply formfibrous projections 2 without use of an adhesive or the like, and alsoto enhance thermal resistance. In the meantime, due to non-use of theadhesive or the like which may contain a substance to become impuritiesfor the silicon structure, it is possible to realize a silicon structurewith impurities or the like not mixed therein.

Moreover, foregoing fibrous projections 2 are preferably previouslyformed in moquette form or mesh form on the surface of silicon substrate1. It is thereby possible to make a surface area per unit area verylarge, so as to enhance the hydrophilicity and the water retentivity.

It is preferable that an optimal length of fibrous projections 2 be inthe range of not smaller than 1.0 μm and not larger than 200 μm, and aspacing at which fibrous projections 2 are joined be in the range of notsmaller than 1 μm and not larger than 10 μm. When the length is smallerthan 1.0 μm or the spacing is smaller than 1 μm, it is only that acondition for producing fibrous projections 2 becomes difficult, and thewater retentivity remains almost unchanged. Moreover, when the lengthexceeds 200 μm, fibrous projections 2 are apt to be broken. When thespacing exceeds 10 μm, the water retentivity slightly decreases.Therefore, as described above, increasing the length and reducing thespacing can enhance both the hydrophilicity and the water retentivity.

Then, a thickness of these fibrous projections 2 is preferably notsmaller than 0.01 μm and not larger than 1 μm. This thickness can beappropriately selected from the viewpoint of the productivity andstrength. The numerical range can be decided based upon a degree ofrequired performance of the device, such as holding of highhydrophilicity or water retentivity, or both high hydrophilicity andwater retentivity, desired to be imparted to the area where fibrousprojections 2 are formed.

Further, these fibrous projections 2 are densely formed as entwined withone another in a moderately curled state. Moreover, the spacing betweenbranch sections of fibrous projections 2 is in the range of not smallerthan 1.0 μm and not larger than 10 μm. When the spacing exceeds 10 μm,fibrous projections 2 are less apt to be entwined with one another.

The numerical ranges of the density and the spacing are also decidedbased upon the degree of the hydrophilicity and the water retentivitydesired to be imparted, in a similar manner to the case of the thicknessmentioned above. It is to be noted that, when fibrous projections 2 areformed by foregoing thermal oxidation, as described later, fibrousprojections 2 become amorphous, and thus apt to be curled. The methodfor producing fibrous projections 2 by thermal oxidation at this timecan be controlled, for example by means of a temperature in thermaloxidation, a gas concentration, or the like.

Further, fibrous projections 2 can also be formed so as to be branchedoff in random directions. In this manner, the hydrophilicity and thewater retentivity can further be enhanced. Fibrous projections 2 made ofamorphous, having been subjected to thermal oxidation by plasma CVD(Chemical Vapor Deposition) on conditions of a predeterminedtemperature, gas concentration, and the like, can be formed as branchedoff in random directions.

FIG. 3 is a diagram showing a result of an X-ray analysis on fibrousprojections 2 of the silicon structure in the first embodiment of thepresent invention. An abscissa axis represents an X-ray diffractionangle 20, and an ordinate axis represents an intensity of a diffractionpeak in arbitrary units.

In FIG. 3, a peak of fibrous projections 2 is strongly indicated at 47degrees, which is a peak of Si (110), and no other peaks are found.Further, since being able to be formed by thermal oxidation, fibrousprojections 2 is considered to be made of amorphous silicon dioxide anddirectly joined to surface 1 a of silicon substrate 1. It should benoted that fibrous projections 2 made of amorphous silicon dioxide havesmaller elasticity than single crystal silicon dioxide as describedlater, and hence are soft and resistant to breaking.

Next, the method for manufacturing the silicon structure in the firstembodiment of the present invention is described with reference to thedrawings. FIGS. 4 to 8 are sectional views showing manufacturing stepsfor explaining the method for manufacturing the silicon structure in thefirst embodiment of the present invention.

First, as a preparatory step, silicon substrate 1 is prepared as shownin FIG. 4. At this time, the surface of silicon substrate 1 ispreferably in a state where silicon atoms are exposed. However, sincethe surface of silicon substrate 1 with the silicon atoms exposed is aptto be oxidized in the air, silicon dioxide is often formed on surface 1a. Therefore, in use of silicon substrate 1, it is desirable to use onewhere silicon dioxide formed on surface la by native oxidization has asmall film thickness.

Subsequently, as shown in FIG. 5, resist film 3 is formed such that onlypredetermined area 1 b is exposed. For this resist film 3 used can be amaterial such as a photoresist typically used for the photolithographytechnique. This exposed predetermined area 1 b is an area where fibrousprojections 2 made of silicon dioxide are selectively formed in a laterstep, and can be selected as an arbitrary area.

Further, areas other than the area where the silicon atoms are exposedare covered with a silicon dioxide thin film in the preparatory step, sothat the area where the silicon atoms are exposed can be selectivelyformed. For example, after a silicon oxide film with a small filmthickness is previously formed on surface 1 a of silicon substrate 1,the area covered with the silicon dioxide thin film is covered with aresist film or the like, and the silicon dioxide thin film inpredetermined area 1 b is removed by etching or the like, so that thearea where the silicon atoms are exposed can be formed.

Thereafter, as a first step, as shown in FIG. 6, seed layer 4 containingC, F and H elements is formed in predetermined area 1 b on siliconsubstrate 1. This seed layer 4 is a layer made of an organic polymercontaining C (carbon), F (fluorine) and H (hydrogen) elements. It is tobe noted that H elements are not essential, and seed layer 4 containingC and F elements may be used. This seed layer 4 can be formed bydissolving at least any gas among fluorocarbon-based gases, such as CF₄,CHF₃, C₂F₆, C₃F₈ and C₄F₈, in plasma by plasma CVD method.

The foregoing fluorocarbon-based gas is dissolved in plasma into a statewhere bonds are cut off, such as CF, CF₂ and CF₃, and these are addedwith H atoms for recombination, to establish polymer molecules in avariety of combinations. However, in order to form fibrous projectionsmade of silicon dioxide in a later step, the order of combination arraysof these molecules contained in seed layer 4 is not particularlyimportant, and the molecules may just be formed in the state of C, H, Fbeing combined.

The reason for this is presumed to be that, since firing is performed inan oxygen atmosphere at a temperature in the range of 1000° C. to 1100°C. in a later step, molecules in any combination arrays are decomposeddue to high heat, and a decomposed matter generated at this time acts topromote generation of the fibrous projections.

Therefore, C, H and F elements at this time are not particularlyrestricted here since a large number of molecules of C, H and F elementsare established as molecules in diverse combinations.

Subsequently, as shown in FIG. 7, resist film 3 is removed. It should benoted that in the process for removing resist film 3 at this time, sucha removal method as to make seed layer 4 remain is required. In thisregard, the method for forming seed layer 4 by plasma CVD method as inthe first embodiment of the present invention is of excellence. In otherwords, the organic polymer film formed by plasma CVD method hasrelatively strong medicine resistance, leading to expanded selections ofmedicines for removing resist film 3.

Further, since this seed layer 4 has the medicine resistance, it is alsopossible to form seed layer 4 and then process silicon substrate 1through use of this seed layer 4 as a resist film.

Next, as a second step, as shown in FIG. 8, silicon substrate 1 whereseed layer 4 is formed is fired in the oxygen atmosphere at atemperature in the range of 1000° C. to 1100° C. Thereby, plural fibrousprojections 2 made of silicon dioxide can be formed only inpredetermined area 1 b where seed layer 4 is formed. These fibrousprojections 2 are bonded to silicon substrate 1 in the state of beingdirectly joined thereto.

As described above, the method for manufacturing the silicon structureaccording to the present invention includes: the first step of formingseed layer 4 made of the organic polymer in the arbitrary area onsilicon-made surface 1 a of silicon substrate 1; and the second step offorming plural fibrous projections 2 made of silicon dioxide in the areawhere seed layer 4 has been formed by heating silicon substrate 1 in theoxygen atmosphere.

With such a method performed, plural fibrous projections 2 can be formedby direct joining in arbitrary predetermined area 1 b on surface 1 a ofsilicon substrate 1, so that silicon dioxide that forms plural fibrousprojections 2 has a large surface area. It is thereby possible tomanufacture a silicon structure capable of exerting at least eitherhydrophilicity or water retentivity which is high as a whole.

More specifically, in predetermined area 1 b where these fibrousprojections 2 are formed, each one of fibrous projections 2 made ofsilicon dioxide has the hydrophilicity, and formed in large number inmoquette form or mesh form. Thereby, even when slight surfacecontamination is generated in the area where fibrous projections 2 madeof silicon dioxide are formed, silicon dioxide that forms fibrousprojections 2 has a large surface area. Therefore, the silicon structureformed in this manner can exert at least either the hydrophilicity orthe water retentivity which is high as a whole.

It is to be noted that in the foregoing manufacturing method, in thesecond step, silicon dioxide thin film 5 is formed on surface 1 a ofsilicon substrate 1 where resist film 3 have been formed, in addition tofibrous projections 2 made of silicon dioxide, and this silicon dioxidethin film 5 also has the hydrophilicity.

In a case where the configuration of the silicon structure as thusdescribed is not preferred, it is possible to manufacture the siliconstructure with the silicon atoms exposed in areas other thanpredetermined area 1 b where fibrous projections 2 are formed by such amanufacturing method as follows. Next, the method for manufacturing thesilicon structure is described with reference to FIGS. 9 to 12.

First, as shown in FIG. 9, fibrous projections 7 made of silicon dioxideare formed on at least one surface of silicon substrate 6 where siliconatoms are exposed on surface 6 a. This formation method is that, as hasalready been described, seed layer 4 containing C, H and F is formed onthe whole surface of silicon substrate 6, and then fired in the oxygenatmosphere at 1000° C. to 1100° C., to allow the formation.

Next, as shown in FIG. 10, resist film 8 is patterned to be formed in anarea where fibrous projections 7 made of silicon dioxide are desired tobe left.

Thereafter, as shown in FIG. 11, fibrous projections 7 made of silicondioxide are etched using an etching solution of HF, BHF or the like.This is because, as the etching solution for use in this etching, it ispreferable to use an etching solution capable of etching silicon dioxidebut not capable of etching silicon. Therefore, as such an etchingsolution, the etching solution of HF, BHF or the like is used.

Next, as shown in FIG. 12, resist film 8 is removed using a resistremover or the like. It is thereby possible to form fibrous projections7 made of silicon dioxide only in predetermined area 6 b.

Further, in the foregoing series of manufacturing steps, from the factthat fibrous projections 7 are bonded with silicon substrate 6 withlarge mechanical strength to prevent a substance that inhibits thehydrophilicity from lying on the interface, it is considered thatfibrous projections 7 are covalently bonded to silicon-made surface 6 aof silicon substrate 6. Thereby, as described above, fibrous projections7 have strong resistance to an acidic or alkaline solvent and an organicsolvent, and can be easily formed in arbitrary predetermined area 6 b onsurface 6 a of silicon substrate 6.

It should be noted that in this method, the shape of fibrous projections7 made of silicon dioxide may be destroyed at the time of removal ofresist film 8, for example in the case of the length of fibrousprojections 7 exceeding 200 μm. Therefore, caution needs to be takenwith a viscosity, a film thickness, a drying method, a removal method,and the like regarding the resist agent that forms resist film 8.

By such a manufacturing method, it is possible to manufacture thesilicon structure having only fibrous projections 7 in predeterminedarea 6 b of silicon substrate 6 without formation of silicon dioxidethin film 5.

As described above, the silicon structure of the present invention isconfigured of silicon with a silicon wafer used as a base substrate,whereby it is possible to realize high processability, three-dimensionalstructure having, for example, a fine groove, hole, concavity, and thelike. Further, it is possible to selectively form the silicon structuresuch that the silicon atoms are partially exposed, thereby to form thestructure by selectively directly joining one ends of the fibrousprojections made of silicon dioxide only to the portion where thesesilicon atoms are exposed.

Moreover, in the area where these fibrous projections are formed, it ispossible to realize an area having at least either the hydrophilicity orthe water retentivity which is extremely high. Since the siliconstructure having the hydrophilicity and the water retentivity isrealizable in such a selectively restricted area, it is possible toapply the silicon structure to devices required to partially have thehydrophilicity or the water retentivity, even through in complex shape,such as a variety of silicon devices including a biosensor, a chemicalreaction chip, and a fluid control device.

Second Embodiment

FIG. 13 is a sectional view of a cellular electrophysiological sensor ina second embodiment of the present invention. Sensor chip 14 for thecellular electrophysiological sensor shown in FIG. 13 is provided withthin plate 15 and frame body 16 formed and arranged on this thin plate15. Cell capturing face 19 of this thin plate 15 is formed of silicondioxide layer 20, while frame body 16 is formed of a silicon layer, andplural fibrous projections 22 made of silicon dioxide are directlyjoined to inner wall 16 a of frame body 16. It is to be noted that a topof frame body 16 is open and an inside of frame body 16 is cavity 17.

This sensor chip 14 is formed of a so-called SOI (Silicon on Insulator)substrate obtained by sandwiching a silicon dioxide layer in the form ofa thin film between two silicon layers, and is configured including thesilicon structure shown in the first embodiment.

Specifically, thin plate 15 is made up of a laminated body of: (second)silicon layer 18 to become a bottom surface; and silicon dioxide layer20 to become cell capturing face 19 of thin plate 15 on this siliconlayer 18. Further, frame body 16 is made up of a silicon layer formed onforegoing silicon dioxide layer 20. Moreover, as shown in FIGS. 13 and14, conduction hole 21 that penetrates thin plate 15 in a verticaldirection is formed in this thin plate 15.

Furthermore, in the present embodiment, plural fibrous projections 22made of silicon dioxide are directly joined to almost the whole area ofinner wall 16 a of frame body 16. It is to be noted that fibrousprojections 22 may be formed not in the whole area of inner wall 16 a offrame body 16, but in a partial area as described later.

Moreover, in the present embodiment, for example, silicon layer 18 inthin plate 15 is formed to have a film thickness of about 5.0 μm,silicon dioxide layer 20 is formed to have a thickness of about 2.0 μm,and the silicon layer is formed to have a thickness of about 400 μm.

A diameter and a depth of conduction hole 21 are decided correspondingto a shape of a cell to be captured. Conduction hole 21 shown in FIG. 13is formed with a diameter being about 3 μM and a depth being about 7.0μm. This is because, in the case of capturing a cell with a diameter of10 μm to 20 μm, conduction hole 21 preferably has a diameter of notsmaller than 1 μm and not larger than 5 μm, and a depth of not smallerthan 1 μm and not larger than 10 μm. Further, thicknesses of siliconlayer 18 and silicon dioxide layer 20 in thin plate 15 are alsoappropriately decided corresponding to the shape of the cell to becaptured. However, the thickness of silicon dioxide layer 20 isdesirably at least not smaller than 0.1 82 m for a reason describedlater.

Further, in the present embodiment, the overall length of fibrousprojections 22 is not smaller than 1.0 μm and not larger than 200 μm,the thickness thereof is not smaller than 0.01 μm and not larger than10.0 μm, and the spacing between plural fibrous projections 22 is notsmaller than 1.0 μm and not larger than 10 μm.

Moreover, these fibrous projections 22 are ones having been grown untilbeing minutely wound or curled in order to have a larger surface area,and fibrous projections 22 each have a wavy shape and are densely formedin a mutually entwined state.

Furthermore, in the present embodiment, sensor chip 14 having theforegoing specific configuration is used for the cellularelectrophysiological sensor shown in FIG. 13.

The cellular electrophysiological sensor shown in FIG. 13 is providedwith: sensor chip 14; chip holding plate (holding section) 23 into whichthis sensor chip 14 has been inserted; electrolytic baths 24 a, 24 barranged above and below sensor chip 14; and electrodes 25 a, 25 brespectively arranged in electrolytic baths 24 a, 24 b.

It is to be noted that, although electrolytic baths 24 a, 24 b are usedas a liquid pooling section for arranging an electrolyte and electrodes25 a, 25 b in the present embodiment, electrodes 25 a, 25 b are notnecessarily required to be in contact with electrolytic baths 24 a, 24b.

In other words, these electrodes 25 a, 25 b may not be arranged insideelectrolytic baths 24 a, 24 b, but may be electrically connected to theelectrolyte that fills these electrolytic baths 24 a, 24 b.

Further, although chip holding plate 23 made of a resin is used as onefor holding sensor chip 14 in the present embodiment, a tube of anotherresin, a glass plate, a glass tube, or the like may be used.

Next, an operation of the cellular electrophysiological sensor in thepresent embodiment is described.

First, the insides of above and below electrolytic baths 24 a, 24 bshown in FIG. 13 are respectively filled with an extracellular fluid andan intracellular fluid, while a bubble is kept out, and theextracellular fluid and the intracellular fluid are respectively broughtinto contact with electrodes 25 a, 25 b.

Here, for example in a case of muscle cells of mammals, theextracellular fluid is typically an electrolyte added with K⁺ ions of155 mM, Na⁺ ions of the order of 12 mM, and Cl ions of the order of 4.2mM, and, the intracellular fluid is an electrolyte added with K⁺ ions ofthe order of 4 mM, Na⁺ ions of the order of 145 mM, and Cl ions of theorder of 123 mM. It should be noted that the electrolyte may be asolution other than the foregoing solution, and may be a solutioncontaining ions of Ca²⁺, K⁺, Na⁺, Cl⁻, and the like which are necessaryfor the cell to perform an ion-channel activity and being blendedappropriately with these elements depending upon the kind of cells andion channels.

In this state, it is possible to measure a conduction resistance valueof the order of 100 kΩ to 10 MΩ between electrodes 25 a, 25 b. This isbecause the extracellular fluid or the intracellular fluid isinfiltrated into conduction hole 21, to allow conduction between twoelectrodes 25 a, 25 b through the extracellular fluid and theintracellular fluid.

Next, when cell 26 is charged from a top side of upper electrolytic bath24 a and lower electrolytic bath 24 b is depressurized, cell 26 ispulled to conduction hole 21, to block conduction hole 21. When a cellfilm of cell 26 closely adheres to a periphery of conduction hole 21,electrical resistance between upper and lower electrolytic baths 24 a,24 b comes into a sufficiently high state of being not smaller than 1 GΩ(hereinafter referred to as a “giga-seal state”).

When this giga-seal state can be realized, an electrical path notthrough cell 26 (leak path) can be reduced as much as possible. Hence inthe case of changes in potentials inside and outside cell 26 having beengenerated due to the ion-channel activity of cell 26, even a slightpotential difference or current can be detected.

Next, a method for manufacturing sensor chip 14 in the presentembodiment is described.

First prepared is a so-called SOI substrate obtained by sandwichingsilicon dioxide layer 20 between silicon layer 18 and silicon layer 27,as shown in FIG. 15. As the SOI substrate used is one where silicondioxide layer 20 with a large film thickness of 2.0 μm and silicon layer18 with a film thickness of 5 μm have previously been formed bylamination or CVD.

Silicon layer 18 and silicon dioxide layer 20 are separately dry-etchedto form conduction hole 21, and a portion of silicon layer 27 whichcorresponds to the cavity (portion to become cavity 17 of FIG. 14) isfurther dry-etched, to form the frame body (portion to become frame body16 of FIG. 14).

Subsequently, at least any gas among CF₄, CHF₃, C₂F₆, C₃F₈ and C₄F₈ isdecomposed in plasma, and introduced toward inner wall 16 a of framebody 16 made up of silicon layer 27. Then, as shown in FIG. 16, seedlayer 28 is formed on inner wall 16 a of frame body 16.

This seed layer 28 is a layer made of an organic polymer containing C, Hand F elements, and can be formed by decomposing the foregoingfluorocarbon-based gas, such as CF₄, CHF₃, C₂F₆, C₃F₈ or C₄F_(8,) inplasma by means of plasma CVD.

It is to be noted that, when these gases are to be decomposed in plasma,the use of ICP (Inductive Coupled Plasma) increases a degree ofdecomposition of the gases, thereby to facilitate uniform formation ofseed layer 28.

It should be noted that in order to uniformly form fibrous projectionsformed by means of seed layer 28 in a later step, a surface of siliconlayer 27 where inner wall 16 a of frame body 16 is exposed is desirablymade up of only silicon atoms, but the surface may be in the state ofbeing formed with an extremely thin, naturally oxidized film.

Thereafter, when sensor chip 14 is fired in the oxygen atmosphere in therange of 1000° C. to 1100° C., as shown in FIG. 14, fibrous projections22 made of silicon dioxide are formed on inner wall 16 a (correspondingto an area where seed layer 28 is formed in FIG. 16) of frame body 16.According to this method, these fibrous projections 22 come into thestate of being bonded with inner wall 16 a by direct joining, thereby tohave excellent thermal resistance, as shown in the first embodiment.

Moreover, in this firing step, on a side surface of silicon layer 18 ora surface of silicon layer 27 where seed layer 28 is not formed, thefibrous projections are not formed but a thermally oxidized film (notshown) made of silicon dioxide is formed. Since this thermally oxidizedfilm has electrical insulation, in the present embodiment, a leakcurrent through sensor chip 14 can be reduced, thereby contributing toimprovement in measurement accuracy of the cellular electrophysiologicalsensor.

In addition, in the firing step, it is considered that seed layer 28containing C, H and F elements is destroyed by firing, with no adherenceleft on inner wall 16 a, and an adherence that becomes a factor toinhibit the hydrophilicity is not present.

In the present embodiment, the measurement accuracy of the cellularelectrophysiological sensor can be improved. The reason for this is thatbubbles that are generated inside cavity 17 of frame body 16 can bereduced.

Specifically, as shown in FIG. 37, on the surface of conventional sensorchip 201, thermally oxidized film 212 made of silicon dioxide is formed.In this area where this thermally oxidized film 212 is formed, a liquidmaterial significantly affected by surface tension of silicon dioxide,such as water, is strongly pulled by the area surface, and the surfacethus has the hydrophilicity.

However, the surface of this thermally oxidized film 212 loses thehydrophilicity when contamination from the outside such as the airadheres to the surface. In other words, this is a state where thesurface tension with which the surface pulls water has become smaller.Further, when thermally oxidized film 212 has a small surface area inaddition to this state, it results in a relatively considerable loss ofthe hydrophilicity.

When the hydrophilicity of the inner wall of frame body 204 decreases,for example in filling the inside of cavity 205 with an electrolyte, anair pool cannot be discharged, thus making bubble 213 apt to begenerated. There have thus been cases where this bubble 213 inhibitselectrical conduction as well as infiltration of the electrolyte or amedicine between above and below conduction hole 202, namely betweenelectrolytic baths 207, 208, leading to reduction in measurementaccuracy of the cellular electrophysiological sensor. Further, therehave been cases where the adhesiveness between cell 211 and the openingof conduction hole 202 is inhibited, leading reduction in measurementaccuracy of the sensor.

In the present embodiment, as shown in FIG. 14, inner wall 16 a of framebody 16 is provided with fibrous projections 22 made of silicon dioxide.Further, in an area where these plural fibrous projections 22 areformed, silicon dioxide has an extremely large surface area.

Accordingly, even when the surface tension per unit area becomes smallerdue to adhesion of contamination, the tension that pulls water is hardlylost since the whole surface area is large, resulting in that thesurface can hold high hydrophilicity for a long period of time. As aconsequence, a bubble is less apt to be generated inside cavity 17,thereby allowing improvement in measurement accuracy of the cellularelectrophysiological sensor.

Further, in the present embodiment, since being directly joined to thesurface of frame body 16 made of silicon, fibrous projections 22 can beformed without using an adhesive or the like, so as to enhance thethermal resistance. Moreover, impurities that come out of the adhesiveor the like and cause a measurement error of the sensor are less apt tobe mixed into the cellular electrophysiological sensor.

Further, since fibrous projections 22 in the present embodiment areminutely wound or curled, the surface area further increases, therebycontributing to improvement in hydrophilicity.

Increasing the length of fibrous projections 22 and reducing the spacingtherebetween can further enhance the hydrophilicity and later-describedwater retentivity. Moreover, intertwining each of such fibrousprojections 22 without superposition on near fibrous projection 22 canfurther increase the surface area, to enhance the hydrophilicity.

Furthermore, in the present embodiment, since plural fibrous projections22 are complexly entwined with one another and the spacing therebetweenis as extremely narrow as not smaller than 1 μm and not larger than 10μm, the surface area of silicon dioxide is extremely large, whereby thehydrophilicity is less apt to decrease, consequently making a bubbleless apt to be generated.

Furthermore, in the present embodiment, fibrous projections 22 areintended not to be formed on cell capturing face 19. In other words,fibrous projections 22 can be selectively formed in a predeterminedposition of the silicon layer, and this predetermined position can bearbitrarily set. For this reason, it is possible to prevent formation offibrous projections 22 on cell capturing face 19 of sensor chip 14 madeof silicon dioxide, thereby to maintain the flatness of the surface ofcell capturing face 19.

Therefore, as shown in FIG. 13, it is possible to make cell 26 and cellcapturing face 19 closely adhere to each other so as to be held. Thisenhances the adhesiveness of cell 26 and an opening of conduction hole21, namely the giga-seal state, resulting in improvement in measurementaccuracy of the cellular electrophysiological sensor.

It is to be noted that, when silicon dioxide layer 20 has a filmthickness of at least 1000 Å, fibrous projections 22 are not formed onits surface, and these fibrous projections 22 can be selectively formedon the silicon layer.

Further, when cell capturing face 19 is configured of silicon dioxidelayer 20, since this silicon dioxide layer 20 has high electricalinsulation, a leak current through the surface or the inside of sensorchip 14 can be reduced, so as to improve the measurement accuracy of thecellular electrophysiological sensor.

Moreover, although cell capturing face 19 may be configured of a silicondioxide layer by thermal oxidation, using the silicon dioxide layer inthe SOI substrate as in the present embodiment can facilitate toincrease the thickness of the silicon dioxide layer. Therefore, in anelectrical path through the sensor chip, a stray capacitance componentcan be made very small, thereby to have a significant effect onreduction in leak current.

It is to be noted that, although thin plate 15 is configured of thelaminated body of silicon layer 18 and silicon dioxide layer 20 tobecome cell capturing face 19 in the present embodiment, thin plate 15may, for example, be formed of only silicon dioxide layer 20 as shown inFIG. 17. Further, as shown in FIG. 17, frame body 16 may be arranged onthe under surface of thin plate 15.

In addition, although fibrous projections 22 are formed in almost thewhole area of inner wall 16 a of frame body 16 in the presentembodiment, they may be formed only in a partial area. As methods forpartially forming fibrous projections 22, two examples are cited below.

A first method is that an area where fibrous projections 22 are not tobe formed is previously covered with protective layer 29 made of a resinor silicon dioxide, as shown in FIG. 18, and subsequently, seed layer 28is formed as shown in FIG. 19.

In this case, when, after formation of seed layer 28, protective layer29 is removed as shown in FIG. 20 and firing is then performed in thepresence of oxygen, it is possible to form fibrous projections 22 in anarbitrary area as shown in FIG. 21. At this time, insulative, thermallyoxidized film 30 is formed in the area where seed layer 28 is notformed, so that a leak current through the surface of frame body 16 canbe reduced.

It should be noted that in the case of forming seed layer 28 by plasmaCVD, this seed layer 28 has relatively strong medicine resistance,thereby facilitating selective removal of only protective layer 29 bychemical treatment using a medicine.

Further, since this seed layer 28 has the medicine resistance, afterformation of seed layer 28, it is possible to perform patterningprocessing on seed layer 28 by means of a normal photolithographictechnique. This method is advantageous in that not only patterning onseed layer 28 but also etching processing on frame body 16 can beperformed, so as to form a structure having a more complex shape.

Moreover, as a second method for partially forming fibrous projections22, there exists a method in which fibrous projections 22 are formed oninner wall 16 a of frame body 16 as shown in FIG. 22, and thereafter, anarea where fibrous projections 22 are desired to be left is covered withprotective layer 31 made of a resin, as shown in FIG. 23.

In this case, fibrous projections 22 in the area where the fibrousprojections are desired to be removed may be removed by etching using anormal medicine such as HF or BHF as shown in FIG. 24, and subsequently,protective layer 31 may be removed as shown in FIG. 25. In this case,the foregoing thermally oxidized film is not formed on the exposed face.

It is to be noted that as the method for removing protective layer 31,it is desirable to remove protective layer 31 by chemical treatmentusing a solvent or the like. This is because fine fibrous projections 22are less apt to be broken in the chemical treatment as compared withmechanical treatment.

Third Embodiment

FIG. 26 is a sectional view of a sensor chip in a third embodiment ofthe present invention. The present embodiment is different from thesecond embodiment in that, as shown in FIG. 26, fibrous projections 22are formed not only on inner wall 16 a of frame body 16, but also on anunder surface of silicon layer 18 in thin plate 15. Further, in thepresent embodiment, fibrous projections 22 are formed so as to surrounda periphery of conduction hole 21.

This can reduce generation of a bubble also on the under surface of thinplate 15. Specifically, when a bubble is generated on the under surfaceof the thin plate, that bubble is drifted to be located directlyunderneath conduction hole 21, thereby to inhibit electrical conductionbetween the above and below conduction hole 21, or make absorption of acell more difficult. This may result in reduction in measurementaccuracy of the cellular electrophysiological sensor.

As opposed to this, in the present embodiment, since fibrous projections22 capable of holding the hydrophilicity for a long period of time areformed on the under surface of thin plate 15, bubbles that are generatedon the under surface of thin plate 15 can be reduced, thereby leading toimprovement in measurement accuracy of the cellular electrophysiologicalsensor.

Further, in the present embodiment, a phenomenon in which dust isaccumulated inside conduction hole 21 in the manufacturing steps can bereduced, thereby improving the measurement accuracy of the cellularelectrophysiological sensor.

This is because the area with high water retentivity is provided on theperiphery of conduction hole 21 on the under surface of thin plate 15.

Specifically, after being formed by dry-etching or the like, sensor chip14 is subjected to a cleaning step and a drying step, to be mounted inthe cellular electrophysiological sensor.

Here, a cleaning liquid, such as alcohol or water, used in the cleaningstep is left inside minute conduction hole 21 and difficult to dry.Therefore, there have been cases where dust having adhered to thesurface of sensor chip 14 (e.g. residue of a resist mask or a naturaloxidized film) is gradually pulled to the water left inside conductionhole 21 as drying progresses, and drying is performed while the dust isin the state of being accumulated inside conduction hole 21. There hasconventionally been a problem in that this dust makes it difficult toattempt for electrical conduction between the above and below conductionhole 21, or inhibits absorption of a cell, leading to reduction inmeasurement accuracy of the cellular electrophysiological sensor.

As opposed to this, in the present embodiment, hydrophilic fibrousprojections 22 are formed as entwined with each other so as to surroundconduction hole 21 at a predetermined spacing therefrom. Hence the areawhere fibrous projections 22 are formed has very high water retentivity.

Accordingly, in the present embodiment, in the step for drying sensorchip 14, a liquid is held in the area where fibrous projections 22 areformed for a long period of time, and dust is pulled to this area wherefibrous projections 22 are formed as drying of the surface of siliconlayer 18 progresses. This can result in reduction in dust accumulated inconduction hole 21, so as to improve the measurement accuracy of thecellular electrophysiological sensor.

It is to be noted that, although there are respective cases of arrangingcavity 17 of frame body 16 in a lower position and in an upper positionin the step for drying sensor chip 14, the phenomenon in which dust ispulled to water as described above often occurs on the upward face atthe time of drying. Therefore, the present embodiment is effectiveparticularly in effectively preventing accumulation of dust inconduction hole 21 in the case of performing drying with drying cavity17 arranged in the lower position.

It is to be noted that descriptions of the other configurations andeffects that are similar to those of the second embodiment are omitted.

Fourth Embodiment

FIG. 27 is a sectional view of a cellular electrophysiological sensor ina fourth embodiment of the present invention. Sensor chip 113 for thecellular electrophysiological sensor shown in FIG. 27 is provided withthin plate 114 and cylindrical frame body 115 formed and arranged onthis thin plate 114. The top of frame body 115 is open and its inside iscavity 116.

This sensor chip 113 is formed of a so-called SOI substrate obtained bysandwiching a silicon dioxide layer between two silicon layers, and thinplate 114 is made up of a laminated body of silicon layer 117constituting a bottom surface and silicon dioxide layer 118 formed onthis silicon layer 117. Plural fibrous projections 121 made of silicondioxide are directly joined to under surface 117 a of silicon layer 117.It is to be noted that silicon dioxide layer 118 serves as cellcapturing face 113 a on silicon layer 117, and further, frame body 115is made up of a silicon layer formed on foregoing silicon dioxide layer118.

Further, as shown in FIG. 28, in thin plate 114, concave section 119which is formed on the bottom surface side (under surface 117 a side ofsilicon layer 117) and conduction hole 120 which penetrates from adeepest section of this concave section 119 to a top surface of silicondioxide layer 118 are formed.

In the present embodiment, plural fibrous projections 121 made ofsilicon dioxide are directly joined to almost the whole area of undersurface 117 a of silicon layer 117 in thin plate 114. It is to be notedthat these fibrous projections 121 may be formed only in a partial areaas described later.

Further, in the present embodiment, a film thickness of silicon layer117 in thin plate 114 is formed to have a film thickness of about 15 μm,for example, silicon dioxide layer 118 is formed to have a thickness ofabout 2.0 μm, and silicon layer 117 is formed to have a thickness ofabout 400 μm.

Concave section 119 has a semispherical shape with a diameter of about20 μm, and conduction hole 120 has a diameter of about 3 μm and a depthof about 7.0 μm. Here, when conduction hole 120 is to capture a cellwith a diameter of 10 to 20 μm, it desirably has a diameter of notsmaller than 1 μm and not larger than 5 μm, and a depth of not smallerthan 1 μm and not larger than 10 μm. Therefore, when silicon layer 117is excessively thick, concave section 119 may be provided for adjustmentas in the present embodiment.

Further, in the present embodiment, the overall length of fibrousprojections 121 is from not smaller than 1.0 μm and not larger than 200μm, the thickness thereof is not smaller than 0.01 μm and not largerthan 10.0 μm, and the spacing between plural fibrous projections 121 isnot smaller than 1.0 μm and not larger than 10 μm.

Moreover, these fibrous projections 121 are ones having been grown untilbeing minutely wound or curled in order to have a larger surface area,and fibrous projections 121 each have a wavy shape and are denselyformed in a mutually entwined state.

Furthermore, in the present embodiment, foregoing sensor chip 113 isused for the cellular electrophysiological sensor shown in FIG. 27.

The cellular electrophysiological sensor shown in FIG. 27 is providedwith: sensor chip 113; chip holding plate (holding section) 122, intowhich this sensor chip 113 is inserted and which holds a side surface ofsensor chip 113; electrolytic baths 123 a, 123 b arranged above andbelow sensor chip 113; and electrodes 124 a, 124 b arranged respectivelyin electrolytic baths 123 a, 123 b. In addition, even when theseelectrodes 124 a, 124 b are not arranged inside electrolytic baths 123a, 123 b, they may be electrically connected to the electrolyte thatfills these electrolytic baths 123 a, 123 b.

It should be noted that, although chip holding plate 122 made of a resinis used as one for holding sensor chip 113 in the present embodiment, aresin tube formed of another resin, a glass plate, a glass tube, or thelike may be used.

Next, an operation of the cellular electrophysiological sensor in thepresent embodiment is described.

First, the insides of above and below electrolytic baths 123 a, 123 bshown in FIG. 27 are respectively filled with an extracellular fluid andan intracellular fluid, while a bubble is kept out, and theextracellular fluid and the intracellular fluid are respectively broughtinto contact with electrodes 124 a, 124 b.

Here, for example in a case of muscle cells of mammals, theextracellular fluid is typically an electrolyte added with K⁺]ions of155 mM, Na⁺ ions of the order of 12 mM, and Cl⁻ ions of the order of 4.2mM. Further, the intracellular fluid is an electrolyte added with K⁺ions of the order of 4 mM, Na ions of the order of 145 mM, and Cl⁺ ionsof the order of 123 mM.

In this state, it is possible to measure a conduction resistance valuein the range of the order of 100 kΩ to 10 MΩ between electrodes 124 a,124 b. This is because the extracellular fluid or the intracellularfluid is infiltrated into conduction hole 120, to allow conductionbetween two electrodes 124 a, 124 b through the extracellular fluid andthe intracellular fluid.

Next, when cell 125 is charged from a top side of upper electrolyticbath 123 a and lower electrolytic bath 123 b is depressurized, cell 125is pulled to an opening (corresponding to opening 120 a of FIG. 28) ofconduction hole 120, to block opening 120 a of conduction hole 120, anda cell film closely adheres to a periphery of conduction hole 120.Thereby, electrical resistance between this opening 120 a and a lead-outport (corresponding to lead-out port 120 b of FIG. 28), namely betweenupper and lower electrolytic baths 123 a, 123 b, comes into asufficiently high state of being not smaller than 1 GΩ](hereinafterreferred to as a “giga-seal state”).

When this giga-seal state can be realized, an electrical path notthrough cell 125 becomes almost nonexistent. Hence in the case ofchanges in potentials inside and outside cell 125 having been generateddue to the ion-channel activity of cell 125, even a slight potentialdifference or current can be measured with high accuracy.

Next, a method for manufacturing the sensor chip in the presentembodiment is described.

First prepared is a so-called SOI substrate obtained by sandwichingsilicon dioxide layer 118 between silicon layer 117 and silicon layer126, as shown in FIG. 29. As the SOI substrate used is one where, forexample, silicon dioxide layer 118 with a large film thickness of theorder of 2.0 μm has previously been formed by lamination or the like.

Therefore, as shown in FIG. 30, mask 127 is placed on silicon layer 117.It should be noted FIG. 30 represents only a thin-plate portion(corresponding to thin plate 114 of FIG. 28) made up of silicon layer117 and silicon dioxide layer 118, omitting a silicon layer(corresponding to silicon layer 126 of FIG. 29) to become a frame body(corresponding to frame body 115 of FIG. 28).

Next, as shown in FIG. 31, an etching gas is sprayed from the above ofmask 127 by dry etching technique, to form concave section 119 at thecenter of silicon layer 117.

As the gas used at this time, a gas for selectively etching silicon isused, and examples thereof may include SF₆, XeF₂ and a mixed gas ofthese gases. Since these gases act to promote etching of silicon in ahorizontal direction as well as a depth direction, silicon layer 117 canbe etched into semispherical saucer shape.

Further, as the above etching gas, a gas in mixture of carrier gasessuch as N₂, Ar, He and H₂ is used. Moreover, a molar ratio of theetching gas to the carrier gas is desirably not larger than 2.0.

Next, as shown in FIG. 32, by the dry etching technique using ICPplasma, a gas (hereinafter referred to as “promotion gas”) for promotingetching of silicon and a gas (hereinafter referred to as “suppressiongas”) for suppressing the etching are alternately introduced from theabove of mask 127, to form conduction hole 120 in silicon layer 117.

As the suppression gas, for example, C₄F₈ or CHF₃ is preferably used. Inthis step, silicon layer 117 is etched during introduction of thepromotion gas, and a protective film is formed on an inner wall of anetched portion during introduction of the suppression gas. Therefore,optimizing the combination of these etching gases leads to the progressof etching only immediately under a mask hole of mask 127, therebyallowing the etching processing from the deepest section of concavesection 119 to conduction hole 120 in almost vertical shape.

It should be noted that, since etching rates are different betweensilicon layer 117 and silicon dioxide layer 118, silicon dioxide layer118 functions as an etching stopping layer, so that conduction hole 120having a predetermined depth can be formed with high accuracy.

Subsequently, mask 127 is removed, and a surface of silicon layer 117 isexposed, as shown in FIG. 33. In addition, silicon layer 117 exposed atthis time is desirably made up of only silicon atoms, but may be in astate where an extremely thin natural oxidized film is formed.

Next, at least any gas among CF₄, CHF₃, C₂F_(s), C₃F₈ and C₄F₈ aredecomposed in plasma, and introduced from a surface of silicon layer117. Then, as shown in FIG. 33, silicon dioxide layer 118 is selectivelyetched, to form conduction hole 120.

Further, in this step, when the gas is introduced to all over thesurface of silicon layer 117, seed layer 128 is formed all over thissurface.

This seed layer 128 is a layer made of an organic polymer containing C,H and F elements, and can be formed by decomposing the foregoingfluorocarbon-based gas, such as CF₄, CHF₃, C₂F₆, C₃F₈ or C₄F_(8,) inplasma by means of plasma CVD.

As described above, after the thin plate (corresponding to thin plate114 of FIG. 28) portion has been formed, the silicon layer(corresponding to silicon layer 126 of FIG. 29) to become the frame body(corresponding to frame body 115 of FIG. 28) is dry-etched, to formframe body 115. Since this step is the dry-etching method using ICPplasma as in the step for forming conduction hole 120 in silicon layer117, a description thereof is omitted.

Subsequently, when sensor chip 113 is fired in the oxygen atmosphere ata temperature in the range of 1000° C. to 1100° C., as shown in FIG. 28,fibrous projections 121 made of silicon dioxide are formed on undersurface 117 a (corresponding to the area where seed layer 128 is formedin FIG. 33) of silicon layer 117. According to this method, thesefibrous projections 121 come into the state of being bonded with siliconlayer 117 by direct joining, thereby to have excellent thermalresistance.

Moreover, in this firing step, on a side surface of silicon layer 117 ora surface of silicon layer 126 where seed layer 128 is not formed,fibrous projections 121 are not formed but a thermally oxidized film(not shown) made of silicon dioxide is formed. Since this thermallyoxidized film has electrical insulation, in the present embodiment, aleak current through sensor chip 113 can be reduced, therebycontributing to improvement in measurement accuracy of the cellularelectrophysiological sensor.

In addition, in the firing step, it is considered that seed layer 128containing C, H and F elements is destroyed on the surface of siliconlayer 27 by firing and thus not being a factor to inhibit thehydrophilicity.

It is to be noted that, although fibrous projections 121 are formed inalmost the whole area of under surface 117 a of silicon layer 117 in thepresent embodiment, they may be formed only in a partial area. In thiscase, for example as shown in FIG. 34, after formation of fibrousprojections 121, protective layer 130 made of a resin may be formed inarea 129 where fibrous projections 121 are wished to be left. Next,fibrous projections 121 in area 131 where fibrous projections 121 arewished to be removed may be removed by etching, using a normal medicinesuch as HF or BHF, and protective layer 130 may then be removed. In thiscase, the foregoing thermally oxidized film is not formed on the exposedface.

It is to be noted that as the method for removing protective layer 130,it is desirable to remove protective layer 130 by chemical treatment.This is because fine fibrous projections 121 are less apt to be brokenin the chemical treatment as compared with mechanical treatment.

In the present embodiment, the measurement accuracy of the cellularelectrophysiological sensor can be improved.

The reason for this is that bubbles that are generated on under surface117 a of silicon layer 117 in thin plate 114 can be reduced.

Specifically, as shown in FIG. 38, on the surface of conventional sensorchip 301, thermally oxidized film 310 made of silicon dioxide is formed.In this area where thermally oxidized film 310 is formed, a liquidmaterial significantly affected by surface tension of silicon dioxide,such as water, is strongly pulled by the area surface, and the surfacethus has the hydrophilicity.

However, the surface of this thermally oxidized film 310 loses thehydrophilicity when contamination from the outside such as the airadheres to the surface. In other words, this is a state where thesurface tension with which the surface pulls water has become smaller.Further, when thermally oxidized film 310 has a small surface area inaddition to this state, it results in a relatively considerable loss ofthe hydrophilicity due to adhesion of contamination.

When the hydrophilicity of under surface 303 a of thin plate 303 ofsensor chip 301 decreases, bubble 312 becomes apt to be generated. Here,when this bubble 312 is generated in the vicinity of lead-out port 311of conduction hole 302, or drifted to the vicinity of lead-out port 311,electrical conduction between the above and below conduction hole 302,namely between electrolytic baths 307 a, 307 b, is inhibited. Further,absorption of cell 309 becomes difficult, thereby to inhibit theadhesiveness (giga-sealing properties) between cell 309 and the openingof conduction hole 302.

In the present embodiment, as shown in FIG. 28, under surface 117 a ofsilicon layer 117 is provided with fibrous projections 121 made ofsilicon dioxide. Further, in an area where these plural fibrousprojections 121 are formed, silicon dioxide has an extremely largesurface area.

Accordingly, even when the surface tension per unit area becomes smallerdue to adhesion of contamination, the whole surface area is large. Onthis account, the tension that pulls water is hardly lost, resulting inthat the surface can hold high hydrophilicity for a long period of time.This can lead to improvement in measurement accuracy of the cellularelectrophysiological sensor.

Further, in the present embodiment, since being directly joined to thesurface of silicon layer 117, fibrous projections 121 can be formedwithout using an adhesive or the like, so as to enhance the thermalresistance. Moreover, impurities that cause a measurement error of thesensor (e.g. impurities coming out of the adhesive or the like) are lessapt to be mixed into the cellular electrophysiological sensor.

Further, since fibrous projections 121 in the present embodiment areminutely wound or curled, the surface area further increases, therebycontributing to improvement in hydrophilicity.

Increasing the length of fibrous projections 121 and reducing thespacing therebetween can further enhance the hydrophilicity andlater-described water retentivity. Moreover, intertwining each of suchfibrous projections 121 and near fibrous projection 121 to be denselyformed can further increase the surface area, so as to enhance thehydrophilicity.

Moreover, in the present embodiment, plural fibrous projections 121 arecomplexly entwined, the spacing therebetween is extremely narrow, andthe surface area of silicon dioxide is extremely large, whereby thehydrophilicity is less apt to decrease. As a consequence, even when finebubble seed 119 a is generated in concave section 119 shown in FIG. 28,it does not become large, and a bubble is thus less apt to be generatedon under surface 117 a and the like.

Furthermore, in the present embodiment, fibrous projections 121 areintended not to be formed on cell capturing face 113 a. Specifically,since fibrous projections 121 are selectively formed on the siliconlayer, fibrous projections 121 are not formed on cell capturing face 113a of sensor chip 113 made of silicon dioxide, thereby to maintain theflatness of the surface of cell capturing face 113 a.

Therefore, it is possible to make cell 125 and cell capturing face 113 aclosely adhere to each other so as to be held. This thus enhances theadhesiveness (giga-sealing properties) of cell 125 and opening 120 a ofconduction hole 120, resulting in improvement in measurement accuracy ofthe cellular electrophysiological sensor.

It is to be noted that, when silicon dioxide layer 118 has a filmthickness of at least 1000 Å, fibrous projections 121 are not formed onits surface, and these fibrous projections 121 can be selectively formedon the silicon layer.

Further, when cell capturing face 113 a is configured of silicon dioxidelayer 118, since this silicon dioxide layer 118 has high electricalinsulation, a leak current through the surface or the inside of sensorchip 113 can be reduced, so as to improve the measurement accuracy ofthe cellular electrophysiological sensor. Moreover, although cellcapturing face 113 a may be configured of a silicon dioxide layer bythermal oxidation, using the silicon dioxide layer in the SOI substrateas in the present embodiment can increase the thickness of the silicondioxide layer. Therefore, in an electrical path through sensor chip 113,a stray capacitance component can be made very small, thereby to have asignificant effect on reduction in leak current.

Fifth Embodiment

FIG. 35 is a sectional view of a sensor chip in a fifth embodiment ofthe present invention. The present embodiment is different from thefourth embodiment in that, as shown in FIG. 35, fibrous projections 121are formed in partial area of under surface 117 a of silicon layer 117.In other words, fibrous projections 121 of the present embodiment arenot formed on the inner walls of concave section 119 and conduction hole120. Fibrous projections 121 of the present embodiment are formed so asto surround the periphery of lead-out port 120 b of conduction hole 120and concave section 119 at a predetermined spacing from lead-out port120 b and concave section 119.

Therefore, as in the fourth embodiment, bubbles that are generated belowsensor chip 113 can be reduced, and further, dust that is accumulatedinside concave section 119 or conduction hole 120 can be reduced, so asto improve the measurement accuracy of the cellular electrophysiologicalsensor. This dust reduction effect is detailed later.

As a method for partially forming fibrous projections 121 as in thepresent embodiment, a first method is that, as in the fourth embodiment,after formation of fibrous projections 121, an area where fibrousprojections 121 are desired to be left is covered with a protectivelayer, and fibrous projections 121 are then removed in an area wherefibrous projections 121 are unneeded.

Further, a second method is that, as shown in FIG. 36, area 132 wherefibrous projections are not to be formed is previously covered withprotective layer 133 made of a resin or silicon dioxide, and seed layer128 is then formed. In this case, when, after formation of seed layer128, protective layer 133 is removed and the sensor chip (correspondingto sensor chip 113 of FIG. 3) is fired in the oxygen atmosphere, it ispossible to form fibrous projections 121 in an arbitrary predeterminedarea.

It should be noted that, as in the fourth embodiment, when seed layer128 is formed by plasma CVD, this seed layer 128 has relatively strongmedicine resistance, thereby facilitating selective removal of onlyprotective layer 133 by chemical treatment using a medicine.

Further, since this seed layer 128 has the medicine resistance, afterbeing formed, seed layer 128 can be subjected to patterning processingby means of normal photolithographic technique. This method isadvantageous in that it is possible not only to perform patterning onseed layer 128 but also to perform etching processing on frame body 115,so as to form a structure having a more complex shape.

In the present embodiment, on the under surface of sensor chip 113, dustinside concave section 119 and conduction hole 120 can be reduced, so asto improve the measurement accuracy of the cellular electrophysiologicalsensor.

The reason for this is that the area with high water retentivity isprovided on the periphery of concave section 119 and lead-out port 120 bof conduction hole 120.

Specifically, after being formed by dry-etching or the like, sensor chip113 is subjected to a cleaning step and a drying step, to be mounted inthe cellular electrophysiological sensor.

Here, a cleaning liquid (e.g. alcohol, water, etc.) used in the cleaningstep is left in concave section 119 of sensor chip 113 and insideconduction hole 120, and difficult to dry. Therefore, dust (e.g. residueof a resist mask, natural oxidized film, etc.) having adhered to thesurface of sensor chip 113 is gradually pulled to the water left inconcave section 119 or inside conduction hole 120 as drying progresses.Consequently, there have been cases where drying is performed while thedust is in the state of being accumulated in concave section 119 orinside conduction hole 120. There has conventionally been a problem inthat this dust makes it difficult to attempt for electrical conductionbetween the above and below conduction hole 120, or inhibits absorptionof a cell, leading to reduction in measurement accuracy of the cellularelectrophysiological sensor.

As opposed to this, in the present embodiment, hydrophilic fibrousprojections 121 are formed as entwined with each other so as to surroundconcave section 119 and conduction hole 120 at a predetermined spacingtherefrom. Hence the area where fibrous projections 121 are formed hasvery high water retentivity.

Accordingly, in the present embodiment, in the step for drying sensorchip 113, a liquid is held in the area where fibrous projections 121 areformed for a long period of time, and dust is pulled to the area wherefibrous projections 121 are formed as drying of the surface of siliconlayer 117 progresses. This can result in reduction in dust accumulatedin concave section 119 and conduction hole 120, so as to improve themeasurement accuracy of the cellular electrophysiological sensor.

It is to be noted that there are respective cases of arranging cavity116 of frame body 115 in a lower position and in an upper position inthe step for drying sensor chip 113. The phenomenon in which dust ispulled to water as described above often occurs on the upward face withcavity 116 of frame body 115 directed upward at the time of drying.Therefore, in the present embodiment, it is possible to effectivelyprevent dust from being accumulated in conduction hole 120 by formingfibrous projections 121 on silicon layer 117.

It is to be noted that fibrous projections 121 may be not only formed inband form on the whole area surrounding the periphery of lead-out port120 b of conduction hole 120, but may be interspersed along the wholearea surrounding the periphery. Further, fibrous projections 121 may beformed as interspersed on the whole area surrounding the periphery.

It is to be noted that descriptions of the other configurations andeffects that are similar to those of the fourth embodiment are omitted.

It is to be noted that, although fibrous projections 121 are formed onlyon thin plate 114 in the present embodiment, they may also be formed onthe surface of frame body 115. For example, when fibrous projections 121are formed also on the inner wall of frame body 115, the hydrophilicityinside frame body 115 is enhanced, to suppress generation of a bubble,thereby further improving the measurement accuracy of the cellularelectrophysiological sensor.

Moreover, fibrous projections 121 may also be formed on the sidesurfaces of thin plate 114 and frame body 115.

INDUSTRIAL APPLICABILITY

The silicon structure and the method for manufacturing the sameaccording to the present invention are useful as being applicable to abiosensor device for measuring a biochemical reaction of a cell or thelike, a medicine screening system for performing pharmacologicaldetermination at high speed, a fluid control actuator of an inkjet head,and the like.

Further, the sensor chip of the present invention is capable ofsignificantly improving measurement accuracy of a cellularelectrophysiological sensor and the like, and hence is useful as beingapplicable to, for example, the field of medical care where highaccurate analyses are required, and to other analyses on pharmacologicalreactions of cells, and the like.

1. A silicon structure, comprising: a base; and a plurality of fibrousprojections, which are made of silicon dioxide and directly joined to asilicon-made surface of the base.
 2. The silicon structure according toclaim 1, wherein the fibrous projections are made of amorphous silicondioxide.
 3. The silicon structure according to claim 1, wherein thefibrous projections are covalently bonded to the silicon-made surface ofthe base.
 4. The silicon structure according to claim 1, wherein alength of the fibrous projections is not smaller than 1 μm and notlarger than 200 μm.
 5. The silicon structure according to claim 1,wherein a spacing between the fibrous projections is not smaller than 1μm and not larger than 10 μm.
 6. The silicon structure according toclaim 1, wherein a thickness of the fibrous projections is not smallerthan 0.01 μm and not larger than 1 μm.
 7. The silicon structureaccording to claim 1, wherein the fibrous projections are densely formedas entwined with one another.
 8. The silicon structure according toclaim 7, wherein a spacing between the fibrous projections is notsmaller than 1 μm and not larger than 10 μm.
 9. The silicon structureaccording to claim 1, wherein the fibrous projections branch out inrandom directions.
 10. A method for manufacturing a silicon structure,comprising: a first step of forming a seed layer made of an organicpolymer in an arbitrary area on a silicon-made surface of a base; and asecond step of heating the base in an oxygen atmosphere, to form aplurality of fibrous projections made of silicon dioxide in the areawhere the seed layer is formed.
 11. The method for manufacturing asilicon structure according to claim 10, wherein the seed layer isformed by CVD in which at least any gas among CF₄, CHF₃, C₂F₆, C₃F₈ andC₄F₈ is decomposed in plasma and then laminated.
 12. A sensor chip,comprising: a thin plate having a conduction hole; and a frame bodyarranged on the thin plate, wherein a cell capturing face of the thinplate is formed of a silicon dioxide layer, and the frame body is formedof a silicon layer, and a plurality of fibrous projections made ofsilicon dioxide are directly joined to an inner wall of the frame body.13. A sensor chip, comprising: a thin plate having a conduction hole;and a frame body arranged on the thin plate, wherein the thin plate ismade of a laminated body of a silicon layer and a silicon dioxide layerformed on the silicon layer, and a plurality of fibrous projections madeof silicon dioxide are directly joined to an under surface of thesilicon layer.
 14. The sensor chip according to claim 13, wherein thesilicon dioxide layer forms a cell capturing face.
 15. The sensor chipaccording to claim 13, wherein the fibrous projections are formed at apredetermined spacing from a lead-out port of the conduction hole, so asto surround a periphery of the lead-out port.